This invention relates to materials used to surround composites, laminates and the like during a vacuum bagging operation in which a negative pressure is applied within the bag to compress the composite or laminate during a cure cycle.
The production of various types of laminates or composites requires the application of external pressure. For example, in the manufacture of safety windows for vehicles, a plastic film is sandwiched between a pair of glass sheets, and the assembly is compressed and heated to complete the laminate. If the surfaces of the laminate are flat, then flat platens may be employed. If the surfaces are curved or irregular, resort is often made to a vacuum bagging technique.
In conventional vacuum bagging, an impervious or non-porous envelope or bag of flexible material is disposed around the assembly to be laminated. The envelope or bag is connected to a vacuum pump, and air is evacuated, causing pressure or compressive forces to be applied to the assembly. Often, a separate, porous, breather fabric is inserted between the bag and the article to facilitate withdrawal of residual gas and to provide release properties. Conventionally, the release or breather layer has included, for example, glass fabrics coated with polytetrafluoroethylene and is porous throughout its thickness.
Various types of release or breather sheets are disclosed in the following U.S. Pats. Nos.: 3,666,600; 4,062,917; 4,216,047; 4,353,855; and 4,548,859. In the latter patent, a breather material is disclosed, which includes a ribbed fabric and a silicone rubber coating. Both the fabric and rubber layers are porous, and a separate impervious bag is disposed around the breather material to complete the assembly.